The invention relates generally to planar waveguides, and more specifically, it relates to a process of fabricating a damascene optical dielectric waveguide.
Present methods of planar waveguide formation on substrates consist of a thin film deposition of the waveguide material and subsequent patterning of the material using lithography and an etching process to transfer the pattern from a resist layer into the waveguide material.
Patented art of interest includes the following U.S. patents, the disclosures of which are incorporated herein by reference:                U.S. Pat. No. 6,775,453 issued to Allman,        U.S. Pat. No. 6,480,643 issued to Hornbeck, and        U.S. Pat. No. 6,324,313 issued to Allman        
The Hornbeck reference describes a graded index of refraction optical waveguide is formed in interlayer dielectric material located above a substrate an integrated circuit-like structure. The waveguide includes a refractive layer of optically transmissive material surrounding a core of optically transmissive material within a trench in the dielectric material.
The second Allman patent describes an optical waveguide extends vertically within the interior of an IC-like structure to route optical signals between horizontal waveguides in different layers of horizontal optical interconnects. A light reflecting structure is positioned at the intersection of the horizontal and vertical waveguides to reflect the light.
In both Allman patents, the waveguide is formed with a light reflective structure at an intersection of the horizontal and vertical waveguides, and the waveguide is completed using damascene fabrication techniques.
As pointed out by Hornbeck the typical waveguide is formed of light transmissive material which is surrounded by an opaque cladding material. Optical signals propagate through the channel, guided by the cladding material. As the optical signals propagate through a particular waveguide, the signals impinge on the cladding material. If the index of refraction of the cladding material is lower than the index of refraction of the material within channel, the majority of the impinging light signal reflects from the cladding material and back towards the center of the channel. Thus the signal propagates through the channel as a result of reflection at the interface of the cladding material. While damascene fabrication steps are typically used in building electrical integrated circuits, these techniques may also be applied to optical waveguide fabrication, as discussed below.